1. Field of the Invention
Aspects of the present invention relate to a fuel cell stack structure that is formed by stacking membrane electrode assemblies (MEAs) and flow channel plates, and more particularly, to a fuel cell stack structure in which a flow channel plate, which is also called a bipolar plate, conventionally formed of graphite or a metal can be replaced by a simple separation plate.
2. Description of the Related Art
A fuel cell is an electricity generator that changes chemical energy of a fuel into electrical energy through a chemical reaction. A fuel cell can continuously generate electricity as long as the fuel is supplied. FIG. 1 is a schematic drawing illustrating the energy transformation structure of a conventional fuel cell. Referring to FIG. 1, when air that includes oxygen is supplied to a cathode 1 and a fuel containing hydrogen is supplied to an anode 3, electricity is generated by a reverse reaction of water electrolysis through an electrolyte membrane 2. However, the electricity generated by a unit cell does not produce sufficient voltage to be used individually. Therefore, electricity is generated by a stack in which a plurality of unit cells is connected in series.
FIG. 2 is an exploded perspective view illustrating a structure of a conventional unit cell mounted in a stack. Referring to FIG. 2, the unit cell in a stack has a structure in which electrodes 1 and 3 and an electrolyte membrane 2 are located between a pair of bipolar plates 10. Reaction flow channels 11, through which hydrogen or oxygen to be supplied to the electrodes 1 and 3 flows, are formed in both sides of each bipolar plate 10. Hydrogen and oxygen are externally supplied to the electrodes 1 and 3 through the reaction flow channels 11. The flow channel plate 10 is called a bipolar plate as the flow channels are respectively formed on both sides of the flow channel plate 10. Repeated stacking of unit cells results in the forming of a stack. Here, a membrane electrode assembly (MEA) 20 includes the cathode and anode electrodes 1 and 3 and the electrolyte membrane 2. A gasket 30 seals an inner space of the unit cell so that hydrogen and oxygen cannot leak outside.
The bipolar plate 10 on which flow channels are formed in both sides thereof is mainly formed of graphite. In such case, there is a high possibility that the bipolar plate 10 can be damaged due to its brittleness when stress is applied to the bipolar plate 10 for a period of time. To solve this problem, the bipolar plate 10 is formed of a metal. However, when the bipolar plate 10 is formed of a metal, there is a handling problem due to the heavy weight of the resultant stack. In order to form flow channels in both sides of the bipolar plate 10, the bipolar plate 10 formed of graphite or a metal the bipolar plate 10 must have a thickness of at least 1 mm; and when a plurality of bipolar plates 10 are stacked, the volume of the stack is large. Also, if the bipolar plate 10 is formed of a metal and used for a period of time, current collection efficiency is reduced due to corrosion of the metal bipolar plate 10. To prevent the decrease in current collection efficiency, it is effective to coat Au on electrical paths. However, in when the electrical paths are coated with Au, the entire bipolar plate 10 must be coated with Au since the bipolar plate 10 itself is an electrical conductor acting as an electrical path. Receiving spaces 12 formed in the bipolar plates 10 are connected to an inlet 10a and an outlet 10b of the bipolar plates 10 so that the oxidizer or fuel can enter and leave the reaction flow channels 11 and contact the cathode 1 and the anode 3 of the MEA 20.
Accordingly, there is a need to develop a fuel cell stack structure in which a stack can be formed having a simple configuration.